Correlation between δ13C and δ15N in C4 and C3 plants of natural and artificial sand-binding microhabitats in the Tengger Desert of China

Carbon isotope ratio (δ13C) and nitrogen isotope ratio (δ15N) of leaf in shrubs and overground matter in herbage were measured on plant species occurring in different aged artificial sand-binding microhabitats, as well as in natural habitat at the south-eastern margin of the Tengger Desert, China. Both δ13C and δ15N of C3 and C4 plants varied widely (− 28.12 ≤ δ13C (‰) ≤ − 23.77 and − 4.45 ≤ δ15N (‰) ≤ 3.66 for C3 species, respectively; and − 15.79 ≤ δ13C (‰) ≤ − 12.63 and − 7.56 ≤ δ15N (‰) ≤ 1.08 for C4 species, respectively), representing the different photosynthetic pathway (C3/C4) environmental controls. The relative abundance of C4 species increased over the development of the sand-fixing vegetation, and the significant differences among sites in δ15N of C4 plants were found. Among the microhabitats, the isotopic pattern of artificial sand-fixing community is a cluster compared to that of natural vegetation and transitional zones in C4 plants; however, this pattern of C3 plants is different significantly. The biological soil crust had significant effect on δ13C of C3 plants, not for δ13C of C4 plants and δ15N of both C3 and C4 species. Our results also describe a distinct pattern of dual-isotopic signatures, which indicated that a different water-use source and soil nitrogen compartment occurred and may promote the coexistence of different life forms in extreme poor water and nutrients ecosystems. With respect to C4 plants, the gramineous plants based on family — level exhibit obviously negative isotopic values (both δ15N and δ13C) than those of chenopodiaceous plants, indicating a high water-use efficiency of gramineous C4 plants and more 15N depleted, and these differences may be a result of different functional groups of C4 species. For C3 plants, the chenopodiaceous species also show more 15N enrichment than those of plants from other families (e.g. composite, leguminous plants and others). Contrast to previous studies, the δ15N values of leguminous plants were not closer to the δ15N of atmospheric nitrogen gas, indicating that leguminous plants in research region used nitrogen mainly from other N sources such as soil, rain/dust, not mainly from biological fixed nitrogen. The correlation between δ13C and δ15N of C3 plants (except leguminous plants) were negative significantly (P = 0.001), while there were positive relationship between δ13C and δ15N in C3 leguminous plants (P = 0.003) and C4 plants (P < 0.0001), indicating that in the water and nutrient limiting region the carbon and nitrogen discriminations are dependent and linked intimately, and vary with the plant species and photosynthetic pathway.